BOSTON — His arm in a cast and his face swollen, a blase-looking Dzhokhar Tsarnaev pleaded not guilty Wednesday in the Boston Marathon bombing in a seven-minute proceeding that marked his first public appearance since his capture in mid-April.

As victims of the bombing looked on, Tsarnaev, 19, gave a small, lopsided smile to his sisters upon arriving in the courtroom. He appeared to have a jaw injury and there was swelling around his left eye and cheek.

Then, after he leaned in toward a microphone and said, “Not guilty” over and over in a Russian accent, he was led out of the courtroom in handcuffs, making a kissing gesture toward his family with his lips. His sister sobbed loudly, resting her head on a woman seated next to her.

Tsarnaev faces 30 federal charges, including using a weapon of mass destruction to kill, and could get the death penalty if prosecutors choose to pursue it.

The proceedings took place in a heavily guarded courtroom packed not only with victims but with their families, police officers, members of the public and the media.

Tsarnaev looked much as he did in a photo widely circulated after his arrest, his hair curly and unkempt. He appeared nonchalant, almost bored during the hearing. The cast covered his left forearm, his hand and his fingers.

The bombing victims showed little reaction in the courtroom after a federal marshal warned them against any outbursts.

The April 15 attack killed three people and wounded more than 260. Authorities say Tsarnaev orchestrated the bombing along with his older brother, Tamerlan Tsarnaev, who died following a gun battle with police and a furious getaway attempt three days after the attack.

Dzhokhar Tsarnaev was arrested on April 19, captured hiding in a bloodstained boat in a suburban backyard after a huge manhunt that paralyzed much of the Boston area. He was hospitalized with wounds suffered in the shootout.

His two sisters were in court in Muslim garb. One was carrying a baby, the other wiped away tears with a tissue. Tsarnaev’s parents remained back in Russia.

Tsarnaev’s lawyer, Judy Clarke, an expert in death penalty cases, asked that the judge enter not-guilty pleas for him, but U.S. Magistrate Judge Marianne Bowler said: “I would ask him to answer.”

Tsarnaev is also charged in the killing of a Massachusetts Institute of Technology police officer and the carjacking of a motorist during the brothers’ getaway attempt.

Reporters and spectators began lining up for seats in the courtroom at 7:30 a.m. as a dozen Federal Protective Service officers and bomb-sniffing dogs surrounded the courthouse. Four hours before the hearing, the defendant arrived at the courthouse in a motorcade that included a van, a Humvee and a state police car.

A group of about a dozen Tsarnaev supporters cheered as the motorcade arrived. The demonstrators yelled, “Justice for Jahar!” as Tsarnaev is known. One woman held a sign that said, “Free Jahar.”

Lacey Buckley said she traveled from her home in Wenatchee, Wash., to attend the arraignment. Buckley said she has never met Tsarnaev but came because she believes he is innocent. “I just think so many of his rights were violated. They almost murdered an unarmed kid in a boat,” she said.

A group of friends who were on the high school wrestling team with Tsarnaev at Cambridge Rindge and Latin waited in line outside the courtroom for hours, hoping to get a seat.

One of them, Hank Alvarez, said Tsarnaev was calm, peaceful and apolitical in high school.

“Just knowing him, it’s hard for me to face the fact that he did it,” said Alvarez, 19, of Cambridge.

“There was nothing sketchy about him,” said Tsou, adding that he had not formed an opinion on Tsarnaev’s guilt or innocence.

Prosecutors say Tsarnaev, a Muslim, wrote about his motivations for the bombing on the inside walls and beams of the boat where he was captured. He wrote that the U.S. government was “killing our innocent civilians.” He also scrawled: “We Muslims are one body, you hurt one you hurt us all.”

Three people — Martin Richard, 8; Krystle Marie Campbell, 29; and Lingzi Lu, 23 — were killed by the two bombs, which were fashioned out of pressure cookers, gunpowder, nails and other lethal shrapnel. Numerous victims lost legs.

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